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April 16, 1929. N. P. RSHEVSKY OPTICAL SIGNALING DEVICE Filed Oct. 28, 1926 Ampzm er 2 INVENTOR Nico/as P. Rasha va@ ATTORNEY Patnted Apu 16," 1929.

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- Appuoationfiled October as. me. serial n. 144309.

This invention relates to signalng and television systems.

It .is an object of this inventon to roduce L a signal-responsive device which s all b e quickerfin its response to the s almg energy than the devces heretofore own.

' It is a further object of this nventon to produce a signal-controlled llurnnatng means which shall be more rapd n its response to the signal energy than devices heretofore known.

It is a further object of ths nven'ton to produce a varying illumination dev cewhch shall be sufliciently rapid in its varatons to serve the needs of television systems, ultrarapid telegraph systems and similarsystems requiring rapid c anges. v

It is a'further object of this nventon to produce a combination of a mask and-an optical instrument pr'oducmg frnges, n whch the width of the fringes shall be made to vary and the amount of light passing through the mask be controlled by such varaton.

The most rapid response to impressed energy known in nature is the change in the character of the light emitted from certain glowing' bodies when they are sub'ected to electric or magnetic fields. This e ect may' be noticed most readily in connection with glowing bodies which give a spectrum consisting of sharp lines.

The spectrum of such glowing bodies contains lines. which even under very searching examination show only a single wave-length, provided the glowing body is in normal condition.. If, however, such a glowing body be subjected to an electric field or to a magnetic field,'the same lines are found to consist of several nearly equal wave-lengths.

These phenomena, known as the Stark effect and as the Zeeman efect, have been known as laboratory curiosities, butheretofore, no practical use has been made of them. In my invention, I employ the Z'eeman efl'ect or the Stark effeet to cause a' change in the width of fringesproduced by an interferometer. When such fringes are narrow, they may be completely hidden by a mask of appro riate pattern.. When the electric field or the magnetic field, acting upon the source of light, causes the fringes to become wide or to merge into one co'tmuous path of light,

'such mask will no longer obstruct the light but will permit a greater or less portion of it to pass. 5

The variatio in the character of the fringes is 'produced in a small fraction of a micro-seeond after the field is impressed upon the source of li ht, and the fringes return to their normalcaracter just as promptlywhen the field is removed. No other acton controlled by any form of energy suit- 'able for silgnaling is known which is as rapid as this. he changes in the amount of light which passes'the mask may thus be made sufficiently rapid for even the most exacting demands of television systems or other ultrarapid communication methods.

The nvention will be better understood and additional objccts of it will be apparent from the following detailed description and the accompanying drawing, in which,

Fig. 1 is a view, partly in section and partly diagrammatic, of the apparatus as a whole;

Fig. 2 is a similar view of a portion of the apparatus, showing a modification.-

' Fi 3 illustratesthe kind of fringes produce when the light` source is normal;

Fig. 4 illustrates the frin es When the light source is subjected to an ectricor a meg netic field.

The apparatus includes' an interferometer mounted upon a base 1. The interferometer includes the usual half-silvered mirror 2 and cooperating mirrors 3 and 4. The distance from the mirror 2 to the mirror 3 is greater than the distance from themirror 2 to the mirror 4. The diflerence in these distances is 'made as great as it can be without rendering the production of fringes impossible. With certain' light sources, this difference may be as great as ten meters. 'If the desired 'distance between the mirrors 2 and 3 is so great as to make the apparatus unwieldly,

the optical path may be inc'eased without requiring the Physical dimensionsof the instrument to* be large. This may be done most readily by the use of supplemental mirrors, causing the light to travel over the distance 2-3 a plurality of times."

Light is supplied to the interferometer from a light source 5. Preferably, this light source is of a kind that will yield a spectrum having very-sharp lines. The cadmum arc, which, as is well known, gives a very sharp red line, is suitable for this purpose. At

room temperature and atm'ospheric pres sure, the wave-length of this line is 'milled head 8. This adjustment bringsthe selected line of the spectrum upon the slit 11 of the interferometer. Preferably, the 'light is concentrated upon the slit 11, by means of a lens 12, and the light from the slitvis rendered parallel by means of another lens 13.- -P'ovision is made for adjusting the width of the slit 11 and this adjustment is controlled by the milled head 14:.

After passing through the mirror system of the interferometer, the light passes through a lens 16, and the fringes are produced at the focal plane of the lens 16. Positioned in the focal plane of the lens 16 is a mask 17, mounted in guides 18 andadjusted by means controlled by the milled head 19. The mask consists of. alternate transparent and opaque portions extending in the same direction as the fringes. The opaque portions may be strips of metal or pigment or ruled lines u on the surface of a glass plate, or they may e bars of opaque metal. In the latter case, the transparent portions are merely the empty spaces between the bars.

On the other side of the mask 17 from the lens 16, a condensing lens 21 is provided: In the specific application of m invention chosen for illustration, the light s condensed upon a photo-electric cell 22, which controls a translating device, illustrated as a telephone 23. In the form of my invention illustrated in Fig. 1, the light source 5 is'controlled by means of an electric field, The field is produced by a battery 24 and controlled by means of a vacuum tube 25, acting through a' high .resistance 26.'- The telephone 27 which may be at any desired distance, is employed, in the illustration, to indicate any incoming signal. The signal need not be telephonic.

In the form of my invention i'llustrated, in Fig. 2, the incoming signal, represented by the telephone 27 after .being amplified at 28, has the form of a varying current in the coils of an electromagnet 29, the poles of which are closely adj acent to the light source 5.

In the operation of my device, the incoming signal controls the output' of the amplifier 25 in Fig.` 1, or the amfplfier 28 in Fig. 2, and thereby controls the eld of force acting upon the light source 5. In Fig. 1, the field of force is an electric field but, in Fig. 2, itis 'a magnetic field.

Thelight given out by th light source 5 may consist of many wav -1 ngths, but, if a e ect, very strong magnetic fields have beenproper kid of light source has been chosen, one of the wave-lengths will be well separated 'from the other wave-lengths in the light from said source. Consequently, it is easy to so a field of force acts u on the light source,

the light entering the slt 11, instead of bein of a single wave-length, will be of sever nearly equal wave-lengths.

The interferometer produces fringes at the' mask. When the light is'of a 'single wavelength, the fringes will be sharp, clean cut,

narrow bands of light separated by dark spaces. The maskwill be so adjusted that an opa ue portion coincides with each fringe. The lig lt which comes through the lens 16 'will thus be completely stopped by the mask 17 and no light will enter -the lens 21.

u When a field of force acts upon the light source 5, the light entering the slit 11 is no longer homogeneous., but consists of diflerent wave-lengths. Several sets of fringes would, theoretically, be created, but, actually, because the several wave-lengths are nearly equal, instead of several sets of fringes, the fringes are" only broadened. The 'result is illustrated in Fi 4. The difference between this figure and ig. 3 is an attem t to show the different ap earance which the fringes will have when t e field is present. The ncrease in width of the fringes will be in accordance with the intensity of the field at the light source.

'When the fringes have the form illustrated in Fig. 4, light wll pass throu 'h the mask 17 because the opaque portions e? the mask are no lon er of suflicient width to completely cover t e fringes. Light will, therefore, pass throu h the lens 21 and be concentrated upon the p oto-electric 'cell 22. The translating device 23 will respond to this change in the light.

An interterometer will not prod'uce fring'es 'if the diflerence in length of the two optical if the interferometer be built with the dif ference between the distance 2'-'-3 and the distance 2-4 merely great enough-to revent the formation of fringes, a very feeb e field will be suflicient to change the fringes into one continuous band of li ht. "This is'true even when the magnetic fi of the electric field. l

`Heretofore, in investigations of the Zeeman necessary, but, with"`t e interferoneter designed as 'just described the change 'm fmges to a continuous band oilight may be d is used, instead noasoe i produced by even very feeble magnetic fields.

the limit at which fringes are just possible,

the change from fringes to a continuous band of light is a brupt, or nearly abrupt, and correspondence between the impressed field and the width of the fringes is lost. With the two optical paths more nearly equal, this correspondence is readily obtained, but then the Electric field is preferable to the magnetic eld.

The changes in the light which emerges from the lens 21 are very rapid. The changes in the field impressed upon the light source 5 may be very rapid. The system, therefore,

is applicable to signalin methods which requre rapid changes. The system may be employed, for example, for telegraphic communication, in which the dots and dashes are sent at a very much higher speed than has heretofore been practicable, or it may be employed for controlling the illumination from point to point of the reproduced picture in a television system. The changes in light may be made with sufiicient rapidity to correspond to a complete covering of the whole picture in a much smaller time than the of a second heretofore regarded as desirable, but unattainable, in such systems.

It will be evident to those skilled-in the art that many modifications' of this invention are possible without departing from the spirit thereof. I, therefore, do not intendthe spe cific illustrations and description 'given heremeans for subjecting said light source t a' in to be construed as limitations.

I claim as my invention: e t

1. In a device for producing changing illumination, a 'source of light normally having a sharp-line spectrum, means for subjecting said light-source to a field of force, whereby the lines in the spectrum will be less sharp, and means for producing a change in illumination corresponding to said change in sharp- I ness.

2. A source ofvarying illumination, comprising a light source remotely-controlled varying field of force, spectroscopic means forobtaining monochromatic light from said source, an interferometer for' producng fringes from said monochromatic light, and

a mask comprising a series of alternating opaque portions and transparent portions,

said portions corresponding in spacing and position to the fringes, whereby the variations in the field cause corresponding variations in the amount of light passing said mask.

3. A source of varying illumination, comprising a light source, remotely-controlled means for subjecting said light source to a varying field of force, spectroscopic means for obtaining monochromatic light from said source, an interferometer for producing fringes from said monochromatic light, and a mask comprising a series of alternating opaque portions and transparent portions, said opaque portions bein narrower than the greatest width of the ringes and corresponding in spacing and positon to the fringes, whereby variatons in the field cause corresponding variations in the amount of light passing said mask.

4. In a device for producing varying illumination, a source of light, means for producing optical fringes therefrom, means acting on said source to vary the width of the fringes and a mask comprising a series of alternating opaque portions and transparent portions, said opaque portions bein narrower than the greatest width of the ringes and corresponding in spacing and position to the fringes, whereb the variations in the field cause correspon ing variations in the amount of light passing said mask.

5.,In a device for producing changing illumination, a mask comprising a series of opaque strps and intervening transparent strps, a source of light, means to 'cause light from said source to produce fringes in position to be obscured by said opaque strips and means acting upon the source of light to so change the character of the light that a por'- tion thereof will pass through the transparent strips.

6. In a signal translating system, a source of light, means controlled by the signal for impressing a field of forceon said source, means for producing optical fringes :from said source, means for ensuring that changes in the width of said fringes will result in changes in illumination and a translating device controlled b the illumination.

In testimony w ereof, I have hereunto subscribed my name this 21st day of October, 

